In the total joint replacements generally in use today it is the polyethylene component that wears. Joint simulation testing as well as the examination of removed implanted polyethylene components demonstrates evidence of brittle fracture, a potentially serious finding as such wear can be exponentially progressive. This is consistent with the hypothesis that under stress, in serum, polyethylene undergoes a stress enhanced reactivity and deterioration. We propose to study this rate of wear as well as its magnitude by device testing in hip joint simulators. Using blocks of "surgical grade" polyethylene we plan to identify the fractions in serum that contribute to the deterioration of the plastic, to study the kinetics of this reaction with and without stress, the effects of this reaction on the mechanical properties of the polyethylene, and to investigate the role of the Hertzian stresses in provoking this reaction.